    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *     http://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 * Unless required by applicable law or agreed to in writing, software
    012 * distributed under the License is distributed on an "AS IS" BASIS,
    013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 * See the License for the specific language governing permissions and
    015 * limitations under the License.
    016 */
    017package org.apache.commons.configuration2.tree;
    018
    019import java.util.Collection;
    020import java.util.List;
    021import java.util.concurrent.atomic.AtomicBoolean;
    022
    023/**
    024 * <p>
    025 * A specialized {@code NodeModel} implementation that uses a tracked node
    026 * managed by an {@link InMemoryNodeModel} object as root node.
    027 * </p>
    028 * <p>
    029 * Models of this type are useful when working on specific sub trees of a nodes
    030 * structure. This is the case for instance for a {@code SubnodeConfiguration}.
    031 * </p>
    032 * <p>
    033 * An instance of this class is constructed with an
    034 * {@link InMemoryNodeModelSupport} object providing a reference to the
    035 * underlying {@code InMemoryNodeModel} and the {@link NodeSelector} pointing to
    036 * the tracked node acting as this model's root node. The {@code NodeModel}
    037 * operations are implemented by delegating to the wrapped
    038 * {@code InMemoryNodeModel} object specifying the selector to the tracked node
    039 * as target root node for the update transaction. Note that the tracked node
    040 * can become detached at any time. This situation is handled transparently by
    041 * the implementation of {@code InMemoryNodeModel}. The reason for using an
    042 * {@code InMemoryNodeModelSupport} object rather than an
    043 * {@code InMemoryNodeModel} directly is that this additional layer of
    044 * indirection can be used for performing special initializations on the model
    045 * before it is returned to the {@code TrackedNodeModel} object. This is needed
    046 * by some dynamic configuration implementations, e.g. by
    047 * {@code CombinedConfiguration}.
    048 * </p>
    049 * <p>
    050 * If the tracked node acting as root node is exclusively used by this model, it
    051 * should be released when this model is no longer needed. This can be done
    052 * manually by calling the {@link #close()} method. It is also possible to pass
    053 * a value of <strong>true</strong> to the {@code untrackOnFinalize} argument of
    054 * the constructor. This causes {@code close()} to be called automatically if
    055 * this object gets claimed by the garbage collector.
    056 * </p>
    057 * <p>
    058 * As {@code InMemoryNodeModel}, this class is thread-safe.
    059 * </p>
    060 *
    061 * @version $Id: TrackedNodeModel.java 1842194 2018-09-27 22:24:23Z ggregory $
    062 * @since 2.0
    063 */
    064public class TrackedNodeModel implements NodeModel<ImmutableNode>
    065{
    066    /** Stores the underlying parent model. */
    067    private final InMemoryNodeModelSupport parentModelSupport;
    068
    069    /** The selector for the managed tracked node. */
    070    private final NodeSelector selector;
    071
    072    /**
    073     * A flag whether the tracked not should be released when this object is
    074     * finalized.
    075     */
    076    private final boolean releaseTrackedNodeOnFinalize;
    077
    078    /** A flag whether this model has already been closed. */
    079    private final AtomicBoolean closed;
    080
    081    /**
    082     * Creates a new instance of {@code TrackedNodeModel} and initializes it
    083     * with the given underlying model and the selector to the root node. The
    084     * boolean argument controls whether the associated tracked node should be
    085     * released when this object gets finalized. This allows the underlying
    086     * model to free some resources. If used as model within a
    087     * {@code SubnodeConfiguration}, there is typically no way to discard the
    088     * model explicitly. Therefore, it makes sense to do this automatically on
    089     * finalization.
    090     *
    091     * @param modelSupport the underlying {@code InMemoryNodeModelSupport} (must not be
    092     *        <b>null</b>)
    093     * @param sel the selector to the root node of this model (must not be
    094     *        <b>null</b>)
    095     * @param untrackOnFinalize a flag whether the tracked node should be
    096     *        released on finalization
    097     * @throws IllegalArgumentException if a required parameter is missing
    098     */
    099    public TrackedNodeModel(final InMemoryNodeModelSupport modelSupport, final NodeSelector sel,
    100            final boolean untrackOnFinalize)
    101    {
    102        if (modelSupport == null)
    103        {
    104            throw new IllegalArgumentException(
    105                    "Underlying model support must not be null!");
    106        }
    107        if (sel == null)
    108        {
    109            throw new IllegalArgumentException("Selector must not be null!");
    110        }
    111
    112        parentModelSupport = modelSupport;
    113        selector = sel;
    114        releaseTrackedNodeOnFinalize = untrackOnFinalize;
    115        closed = new AtomicBoolean();
    116    }
    117
    118    /**
    119     * Returns the {@code InMemoryNodeModelSupport} object which is used to gain
    120     * access to the underlying node model.
    121     *
    122     * @return the associated {@code InMemoryNodeModelSupport} object
    123     */
    124    public InMemoryNodeModelSupport getParentModelSupport()
    125    {
    126        return parentModelSupport;
    127    }
    128
    129    /**
    130     * Returns the parent model. Operations on this model are delegated to this
    131     * parent model specifying the selector to the tracked node.
    132     *
    133     * @return the parent model
    134     */
    135    public InMemoryNodeModel getParentModel()
    136    {
    137        return getParentModelSupport().getNodeModel();
    138    }
    139
    140    /**
    141     * Returns the {@code NodeSelector} pointing to the tracked node managed by
    142     * this model.
    143     *
    144     * @return the tracked node selector
    145     */
    146    public NodeSelector getSelector()
    147    {
    148        return selector;
    149    }
    150
    151    /**
    152     * Returns the flag whether the managed tracked node is to be released when
    153     * this object gets finalized. This method returns the value of the
    154     * corresponding flag passed to the constructor. If result is true, the
    155     * underlying model is asked to untrack the managed node when this object is
    156     * claimed by the GC.
    157     *
    158     * @return a flag whether the managed tracked node should be released when
    159     *         this object dies
    160     * @see InMemoryNodeModel#untrackNode(NodeSelector)
    161     */
    162    public boolean isReleaseTrackedNodeOnFinalize()
    163    {
    164        return releaseTrackedNodeOnFinalize;
    165    }
    166
    167    @Override
    168    public void setRootNode(final ImmutableNode newRoot)
    169    {
    170        getParentModel().replaceTrackedNode(getSelector(), newRoot);
    171    }
    172
    173    @Override
    174    public NodeHandler<ImmutableNode> getNodeHandler()
    175    {
    176        return getParentModel().getTrackedNodeHandler(getSelector());
    177    }
    178
    179    @Override
    180    public void addProperty(final String key, final Iterable<?> values,
    181            final NodeKeyResolver<ImmutableNode> resolver)
    182    {
    183        getParentModel().addProperty(key, getSelector(), values, resolver);
    184    }
    185
    186    @Override
    187    public void addNodes(final String key, final Collection<? extends ImmutableNode> nodes,
    188            final NodeKeyResolver<ImmutableNode> resolver)
    189    {
    190        getParentModel().addNodes(key, getSelector(), nodes, resolver);
    191    }
    192
    193    @Override
    194    public void setProperty(final String key, final Object value,
    195            final NodeKeyResolver<ImmutableNode> resolver)
    196    {
    197        getParentModel().setProperty(key, getSelector(), value, resolver);
    198    }
    199
    200    @Override
    201    public List<QueryResult<ImmutableNode>> clearTree(final String key,
    202            final NodeKeyResolver<ImmutableNode> resolver)
    203    {
    204        return getParentModel().clearTree(key, getSelector(), resolver);
    205    }
    206
    207    @Override
    208    public void clearProperty(final String key,
    209            final NodeKeyResolver<ImmutableNode> resolver)
    210    {
    211        getParentModel().clearProperty(key, getSelector(), resolver);
    212    }
    213
    214    /**
    215     * {@inheritDoc} This implementation clears the sub tree spanned by the
    216     * associate tracked node. This has the side effect that this in any case
    217     * becomes detached.
    218     *
    219     * @param resolver
    220     */
    221    @Override
    222    public void clear(final NodeKeyResolver<ImmutableNode> resolver)
    223    {
    224        getParentModel().clearTree(null, getSelector(), resolver);
    225    }
    226
    227    /**
    228     * {@inheritDoc} This implementation returns the tracked node instance
    229     * acting as root node of this model.
    230     */
    231    @Override
    232    public ImmutableNode getInMemoryRepresentation()
    233    {
    234        return getNodeHandler().getRootNode();
    235    }
    236
    237    /**
    238     * Closes this model. This causes the tracked node this model is based upon
    239     * to be released (i.e. {@link InMemoryNodeModel#untrackNode(NodeSelector)}
    240     * is called). This method should be called when this model is no longer
    241     * needed. This implementation is idempotent; it is safe to call
    242     * {@code close()} multiple times - only the first invocation has an effect.
    243     * After this method has been called this model can no longer be used
    244     * because there is no guarantee that the node can still be accessed from
    245     * the parent model.
    246     */
    247    public void close()
    248    {
    249        if (closed.compareAndSet(false, true))
    250        {
    251            getParentModel().untrackNode(getSelector());
    252        }
    253    }
    254
    255    /**
    256     * {@inheritDoc} This implementation calls {@code close()} if the
    257     * {@code untrackOnFinalize} flag was set when this instance was
    258     * constructed. While this is not 100 percent reliable, it is better than
    259     * keeping the tracked node hanging around. Note that it is not a problem if
    260     * {@code close()} already had been invoked manually because this method is
    261     * idempotent.
    262     *
    263     * @see #close()
    264     */
    265    @Override
    266    protected void finalize() throws Throwable
    267    {
    268        if (isReleaseTrackedNodeOnFinalize())
    269        {
    270            close();
    271        }
    272        super.finalize();
    273    }
    274}